1. Field of the Invention
The present invention relates to a graphic decoder circuit for a compact disk player, which has a superimposing function of switching pictures based on RGB video signals obtained from a compact disk and pictures based on other video signals thereby to compose the pictures.
2. Description of the Prior Art
In a digital audio disk called a compact disk, signals called subcode signals are recorded in addition to digital audio signals. The subcode signals include information about numbers and counts as well as graphic information about still pictures.
On the other hand, pictures obtained from a personal computer are generally superimposed on pictures obtained from a television receiver or a video tape recorder, and such technique of superimposition is disclosed in, e.g., a magazine "Television Technique" June 1984, pp. 33-38. In such conventional technique, picture switching signals are produced on the basis of whether or not RGB video signals are obtained from a personal computer to switch pictures of the personal computer and those of a television receiver etc., and superimposition cannot be performed on arbitrary color signals in the RGB signals.